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Flow measurements, a changing climate, and Vermont

First New Orleans, then Irene and Sandy, and now Colorado. There is little doubt that there has been a significant increase in extreme weather events, but what does this mean for Vermont? Well, quite a bit. Variable weather and a shifting climate from one decade to the next have a very real impact on our rivers and lakes and, in turn, how rivers, lakes, and wetlands are managed. For example, we cannot expect the same springtime refill rate for our reservoirs now relative to when those rates were first estimated 25 years ago. Likewise, summer low flows may change, requiring that we reconsider how much water is released from those reservoirs in order to maintain summer flows to protect brook trout. So what is the “normal” behavior of a river, and how is that changing? The only way to determine this is by making measurements of river flows… and lots of them.

Thankfully the U.S. Geological Survey (USGS) works to provide this information 24/7/365, for over 70 stream, lake, and groundwater gages throughout Vermont. Once a few years of this data is available (some gages have over 100 years of information), Watershed Management Division scientists can interpret what average conditions look like. Just as flipping a coin one hundred times instead of three gets you closer to the true likelihood of getting heads half of the time, the same goes for additional years of stream flow measurements. We get a more accurate picture of what normal highs, lows, and averages should be expected. With additional years of stream flow measurements, our best estimates from 2006 will be different than those made in 2013. This is especially important now that there is pretty convincing evidence of changes in rainfall patterns and flows. The Division makes regular and ongoing use of the USGS gage data to continually update our understanding of water flows, and the USGS gages help inform flow conditions in all of the other unmeasured watersheds in Vermont. Having good flow information means better management of water resources.

For example, wastewater treatment facilities provide critical pollution control services by treating our communities’ discarded water, thereby preventing public health threats from polluted waters. One important part of proper treatment plant management is knowledge of the flow levels in the receiving stream. This information is used to calculate how much treated wastewater a facility can discharge to the stream, while ensuring high water quality and public use and enjoyment of the receiving streams. The Division’s scientists are currently updating low flow estimates for all streams receiving treated wastewater. All of the newly available flow data collected at the USGS stream gages will allow the Division and the town treatment plant operators to ensure protection of public and ecological health in the midst of a changing climate.